Some of the most significant problems preventing the development of implantable neural protheses for the neurologically handicapped involve long-term insulation and protection of implanted devices. Specifically, micromachined, thin-film recording and stimulating microelectrode probes and miniature wires or cables connecting these electrodes with a source of control and power must be protected from the hostile ionic environment of extracellular fluids for decades if they are to be used reliably in humans. The long-term goal of this research is to develop biocompatible coating systems that will permit these neural prosthetic implants to function reliably over the lifetime of an implant recipient. The current most promising coatings for protection of the bond area of implantable devices are the silicone coatings. However, the bulkiness of the silicone coatings is a problem for many applications. Also, the coatings must be applied by hand, and automating that procedure will not be trivial. A vapor deposited material that performed as well as the silicones would be highly advantageous. Parylene will be deposited onto test structures following various surface pre-treatments and coatings layers. Life tests of parylene coated assemblies will consist of voltage biased saline soaks. Surface resistivity changes will be used as an indicator of the efficacy of various coatings techniques. Silicone elastomer coated test device performance will be used as a relative indicator of the value of the parylene coating techniques.